A wireless communication system transmits and receives a wireless signal by using an assigned frequency resource. In general, a system divides and uses a frequency resource into so-called channel units. For example, in the case of a Global System for Mobile communications (GSM) system, channels are defined as in Table 1 below.
TABLE 1Uplink Sub-BandDownlink Sub-BandNumberBand[MHz][MHz]of CarriersGSM 450450.4-457.6460.4-467.635GSM 480478.8-486  488.8-496  35GSM 850824-849869-894124GSM 900890-915935-960124EGSM 900880-915925-960174RGSM 900876-915921-960194DCS 18001710-17851805-1880374PCS 19001850-19101930-1990299
If a user terminal is powered on, available or accessible channels are scanned, synchronization is achieved in at least one channel that is determined optimal, and then the user terminal accesses a base station. An example of a process of achieving the synchronization of the terminal is briefly described with reference to FIG. 1.
FIG. 1 shows a process of achieving synchronization in a wireless communication system according to the related art.
Referring to FIG. 1, a terminal is powered on in operation 101, and monitors the Radio Frequency (RF) level of each channel through a channel scan in operation 103. Subsequently, the terminal selects a channel having the highest RF level in operation 105, scans the Frequency Correction Channel (FCCH) of the selected channel in operation 107, and determines whether the FCCH is detected, in operation 109. If the FCCH is detected, the terminal scans a Synchronization Channel (SCH) in operation 111 and determines whether the SCH is detected, in operation 113. Since the SCH detection means that synchronization is achieved, the terminal ends this procedure. On the contrary, if the FCCH is not detected in operation 109 or the SCH is not detected in operation 113, the terminal selects a channel having the next priority RF level in operation 115 and returns to operation 107.
As discussed with reference to FIG. 1, measuring RF levels for all channels that are used in a system is needed to achieve synchronization. Since channels are defined on different frequencies, the terminal repetitively measures RF levels while changing the reception band of an RF receiver. The terminal may control the reception band by adjusting a Phase Locked Loop (PLL). In this case, since the adjustment of the PLL is hardware controlled, a certain time is needed for the adjustment and stabilization. Thus, as the number of channels increases, a time needed for channel scan becomes long. For example, referring to Table 1, there are hundreds of channels in the case of GSM system. When approximately 11 frames are needed for one channel scan, a time corresponding to thousands of frames is needed to scan all channels.
As described above, if the terminal is powered on, a long time is needed to scan channels. Thus, after the terminal is powered on, a user may not use a service for a long time. Moreover, as a time taken to scan becomes long, the reliability of a previously scanned RF level decreases. Thus, alternatives for decreasing times taken to scan channels and achieve synchronization are needed.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.